diff --git a/flake.nix b/flake.nix
index 737979f..de821a9 100644
--- a/flake.nix
+++ b/flake.nix
@@ -32,8 +32,7 @@
           ];
         };
 
-        # PostgreSQL 17 with PostGIS installed into PostgreSQL's
-        # extension path.
+        # PostgreSQL 17 with PostGIS in the PostgreSQL extension path.
         postgresql = pkgs.postgresql_17.withPackages (
           ps: [
             ps.postgis
@@ -101,8 +100,9 @@
             # ============================================================
             # Start PostgreSQL
             #
-            # No TCP listener. The development database is accessed
-            # exclusively through the Unix socket in .pgsocket.
+            # PostgreSQL is deliberately restricted to the Unix socket.
+            # No TCP/IP listener is opened, so there are no port conflicts
+            # with another local PostgreSQL instance.
             # ============================================================
 
             if ! pg_ctl \
@@ -116,7 +116,7 @@
               pg_ctl \
                 -D "$PGDATA" \
                 -l "$PGDATA/postgresql.log" \
-                -o "-k $PGHOST" \
+                -o "-c listen_addresses= -k $PGHOST" \
                 start \
                 >/dev/null
             fi